Process for desulfurization of fuel gas

Abstract

Apparatus and a method for removal of acid gases from a first gas rich in carbon dioxide and for desulfurizing a second gas lean in carbon dioxide but containing sulfur compounds as impurities. The method includes contacting the first gas with a solvent capable of extracting carbon dioxide and sulfur compounds from the first gas. Then, the solvent containing carbon dioxide is separated from the solvent containing sulfur compounds. The second gas is then contacted with said solvent containing carbon dioxide under conditions sufficient to cause said solvent containing carbon dioxide to extract sulfur compounds from said second gas and to release carbon dioxide. The desulfurized second gas is thereafter separated from the solvent containing sulfur compounds from the second gas.

We claim: 
     
       1. In a system for removal of acid gases from a first gas rich in carbon dioxide, available at superatmospheric pressure and containing hydrogen sulfide, and a second gas containing carbon dioxide at a partial pressure lower than in said first gas and containing hydrogen sulfide, where said removed acid gases will comprise mainly carbon dioxide and hydrogen sulfide and may have a hydrogen sulfide content below mole 30%, the process comprising the steps of: contacting the first gas in a first absorber having a first stage and a second stage with a first solvent having a high selectivity for hydrogen sulfide in counter-current flow of said solvent and said first gas, a portion of the solvent from the second stage being directed to the first stage, whereby said solvent absorbs hydrogen sulfide and carbon dioxide in the first stage and carbon dioxide but not hydrogen sulfide in the second stage;   recovering a hydrogen rich gas from the second stage of the first absorber;   contacting said second gas in a second absorber with another portion of the solvent from the second stage of the first absorber under conditions sufficient to cause said solvent to extract hydrogen sulfide and to release carbon dioxide from said second gas;   flashing the solvent from the first stage of the first absorber consecutively at an intermediate pressure and a lower pressure;   flashing the solvent separated from the first stage of the second absorber at said lower pressure;   compressing the flashed gases from said intermediate and lower pressure flashes to produce compressed gases rich in both carbon dioxide and hydrogen sulfide;   returning the compressed gases to the second absorber;   stripping the carbon dioxide and hydrogen sulfide from the combined flashed first and second solvents to regenerate a lean solvent; and   recovering an acid gas stream comprising carbon dioxide containing less than 30 mole percent of hydrogen sulfide from the stripped solvents.   
     
     
       2. The process of claim 1, wherein the first absorber is provided with at least one side chiller to remove the heat of absorption of carbon dioxide. 
     
     
       3. In a system according to claim 1, wherein the solvent is methanol. 
     
     
       4. In a system according to claim 1, wherein the solvent is the dimethyl ether of a polyethylene glycol having 3 to 8 ethylene units. 
     
     
       5. In a system according to claim 1, wherein the solvent is N-methyl pyrolidone. 
     
     
       6. In a system according to claim 1, wherein the pressure of the first gas is above 250 psig, the solvent being in the temperature range of -40° F. to 100° F. 
     
     
       7. In a system according to claim 1, wherein the second gas and the solvent containing carbon dioxide move in countercurrent relationship to each other in said second absorber.